C-Fos gene expression pattern in the hypothalamus and the preoptic area ofdefeminized rats

The object of the present study was to determine the c-fos gene expression pattern in the hypothalamus (HYP) and the preoptic area (POA) after estradi ol and testosterone priming during the critical period of sexual differenti ation of the rat brain. Three-day-old female rats were injected s.c. with a single dose of 17 beta-estradiol (200 mu g), testosterone enantate (200 mu g) or vehicle (corn oil). HYP and POA were dissected 2 h, 24 h and 14 days after treatments and on the day of vaginal opening (VO). Other animals, pr eviously treated as above, were acutely injected with 17 beta-estradiol (5 mu g) on the day of VO; HYP and POA were obtained 3 h later. Total RNA was extracted and processed for semiquantitative RT-PCR. We observed that c-fos gene expression was markedly increased in POA of the animals treated with estradiol or testosterone 2 h after treatments, while a non-significant inc rease in c-fos gene expression was observed in the HYP of these animals. We found a significant increase in c-fos expression in HYP and POA on the day of VO in both estradiol and testosterone defeminized rats. Interestingly, the acute estradiol administration on the day of VO did not induce c-fos ge ne expression in either HYP or POA of defeminized animals, instead a diminu tion in its expression was observed in animals treated with testosterone in POA. The overall results suggest that estradiol and testosterone imprintin g during critical postnatal period of sexual differentiation of the brain p ermanently modifies the regulation of c-fos gene expression. (C) 2000 Elsev ier Science B.V. All rights reserved.